1. Field of the Invention
The present invention relates to an improved automotive seat having a side air bag device disposed therein at one side of a seat back frame thereof and including an inflator and an air bag inflatable and expandable out of the seat when supplied with an output pressure from the inflator, and in which a trim cover comprises a central portion and a front side portion and lateral portion on either side of the central portion, those of the front side and lateral trim cover portions which cover together the air bag device being sewn on each other along their neighboring ends to form a seam line, or break line, along which the trim cover is to be broken when the air bag is inflated and expanded.
2. Description of the Prior Art
In a conventional automotive seat incorporating a side air bag device, a sewing thread having a normal strength is used to sew other portions of a trim cover than the neighboring ends of front side and lateral portions covering together the side air bag device while a weaker sewing thread is used to sew on each other the neighboring end portions of the front side and lateral trim cover portions over the air bag device to form a seam line, or break line, along which the trim cover is to be broken when applied with an expansion pressure of the air bag inflated with an output pressure from an inflator. When the air bag is inflated and expanded, the weaker thread used to thread the seam line can easily be cut for the air bag to instantly burst out from the seat inside (as disclosed in the Japanese patent application laid open as a Provisional Publication No. 216820/96, for example).
As mentioned above, the sewing thread used to sew the seam line, or break line, of the trim cover should be easy to cut when the trim cover is applied with the expansion pressure of the inflated air bag. However, the sewing thread should be strong enough to withstand a pressure applied to the trim cover during normal use of the seat. Also, since the trim cover will be elongated at least by nature when pushed outwardly by the inflated air bag, the stress caused by the inflation of the air bag cannot be well concentrated to the seam line, or break line, of the trim cover the moment the air bag is inflated and expanded. If the inflator is set to provide a low output for a soft inflation of the air bag, the trim cover cannot be effectively broken along the break line.
To concentrate the expansion pressure of an air bag to the seam line, or break line, of a trim cover, automotive seats have been proposed in which there is provided on the inner surface of a lateral portion of a trim cover a stay cloth made of a material which is less elongated and one end of which is sewn together with the seam line, or break line, of the trim cover (as disclosed in the Japanese patent applications laid open as Provisional Publication Nos. 71204/'97, 71205/'97 and 123860/'97, for example).
In these conventional seats, however, the stay cloth reinforces only one of, the lateral one, and front side portions of the trim cover, on which the stay cloth extends from the break line. Therefore, the other of the lateral and front side portions of the trim cover which is not reinforced by the stay cloth, cannot be restrained from being elongated when applied with the expansion pressure of the inflated air bag. This is not sufficient enough to instantly concentrate the air bag inflation-caused stress to the break line of the trim cover for quick breakage of a part of the thread used to sew the seam line.
Also, since the air bag is inflated only along the other of the front side and lateral portions of the trim cover which is not reinforced by the stay cloth, the air bag cannot be inflated evenly in a predetermined direction.
In addition, automotive seats with a side air bag device have been proposed which uses, on the inner surface of a front side portion of a trim cover, a stay cloth sewn at one end thereof on an end of the front side portion of the trim cover on which the stray cloth extends from the break line of the trim cover (as disclosed in the Japanese patent applications laid open as Provisional Publication Nos. 39711/'97 and 76868/97', for example). In these conventional automotive seats, however, since only one of the front side and lateral portions of the trim cover over the air bag device is reinforced by the stay cloth, the other of the front side and lateral portions of the trim cover not reinforced by the stay cloth cannot be restrained from being elongated when applied with the expansion pressure of the inflated air bag.